So far, interesterification has been one of the effective means as a method for modifying fats and oils. As this interesterification, there are a chemical procedure, that is, a metal-catalyzing method of random interesterification using, as a catalyst, a substance such as an alkali metal alcoholate, an alkali metal, an alkali metal hydroxide, or the like, and an enzymatic interesterification method of 1,3-position specific or random interesterification using a lipase.
In such interesterification, since fatty acid esters and/or free fatty acids are produced, they are recovered from the reaction product by distillation after completion of the reaction. Then, they are subjected to processing such as hydrogenation, and recycled as fatty acid esters and/or free fatty acids for interesterification in some cases (JP 3-69516 B). For example, in a process for producing a symmetric triglyceride such as cacao butter by enzymatic interesterification between a fat rich in oleic acid as a constituent fatty acid, and a saturated fatty acid ester and/or a free fatty acid using a lipase, it is advantageous to hydrogenate fatty acid esters and/or free fatty acids containing oleic acid as a main component recovered from the reaction product and recycle them as the aforementioned saturated fatty acid ester and/or free fatty acid.
In interesterification processes, there is also such a reaction manner that an interesterification reaction is performed by a one stage to continuous multi-stage manner in order to obtain a reaction product of a processed glyceride fat having high purity. That is, in this manner, an unreacted fatty acid ester fraction is selectively left in a reaction system after the first stage interesterification reaction, and a fresh unreacted fatty acid ester is added thereto, followed by performing the interesterification reaction of the second stage to obtain a reaction product of the processed glyceride fat having high purity, whereby, a subsequent fractionating step becomes unnecessary (WO 96/10643).